In many prior art injection molding machines the outlet of the machine is fitted with a check valve which remains closed during plasticizing of the melt and at the appropriate time is opened by pressing the molding machine against a mold sprue bushing.
That is, the valve usually has only two positions i.e. open or closed.
When it is desired to purge the machine to observe the quality of the melt, for example, it is necessary to introduce a cumbersome, intermediate device at the outlet of the machine opening the check valve partially to allow melt to flow into a purging catchment or similar container.
The introduction of the purging unit is hazardous and difficult to perform quickly to avoid degradation of sensitive resins.
The purging unit is frequently handled manually exposing the operating to hot melt and upon removal the hazard is increased by the heat induced into the purging unit.
Representative prior art purging structures are disclosed and described in U.S. Pats. Nos. 3,374,502, 3,401,426 l and 4,386,903.
While prior art purging units are operable it is highly desirable to simplify the purging operation to reduce operation risk, speed up the process, reduce scrap and to avoid degradation of sensitive resins.